1. Field of the Invention
This invention relates generally to the art of sampling a liquid for the purpose of analyzing the liquid to determine its composition. The invention relates more particularly to novel liquid sampling methods and devices for this purpose.
2. Prior Art
It will become readily evident as the description proceeds that the liquid sampling methods and devices of this invention may be utilized for a variety of liquid sampling purposes and to sample a variety of liquids in a variety of sampling environments. One sampling application of the invention which is of particular importance at the present time involves sampling storm water runoff from industrial property to determine the presence of toxics and other contaminants, if any, in the runoff. Another useful application involves sampling liquid leakage from industrial liquid processing equipment to aid in locating the leak(s). The invention will be described in the context of these particular applications. Other possible uses of the invention will be mentioned and involve sampling liquid in a storm drain system or other liquid conductor, sampling liquid discharge from a sewage treatment plant or an industrial process or the like, and sampling liquid in a body of liquid. The invention may be utilized to sample liquids from any type of fluid conductor including surfaces, open channels, or closed pipes or ducts, and liquids which are either homogenous liquids, mixtures of miscible liquid components, or mixtures of immiscible liquid components.
The water flowing through public storm drain systems often contains toxic and other contaminants which end up polluting large public water bodies, such as the San Diego, Santa Monica, and San Francisco Bays in California. Much of this contamination is due to deliberate and illegal dumping of industrial waste products into the storm drain systems in order to avoid the problems and cost associated with legal disposition of such waste products. The liquid sampling methods and devices of this invention may be utilized to sample the water flowing through these storm drain systems for the purpose of determining the presence and source of such contaminants.
Another extensive source of contamination of the water in storm drain systems is storm water runoff from industrial property and the like. Thus, the ground and other exterior surfaces of such property are often covered by or contain a relatively high concentration of various industrial substances due to spillage of the substances onto the surfaces and the ground, leakage of the substances into the soil from pipes or storage containers, and hosing of the substances from interior floor areas onto exterior surface areas and the ground. During a rainstorm, these substances are entrained in the storm water runoff from the property and are carried with the storm water runoff into the public storm drain system.
In an effort to reduce such storm water runoff pollution, the state of California recently passed legislation establishing a program entitled the Industrial Storm Water Permitting Program. This program requires industrial property owners to obtain a permit, referred to as a General Industrial Storm Water Permit, for storm water runoff or discharge from their properties into the public storm drain system. The permits are issued through the State Water Resources Control Board.
Obtaining such a permit involves the payment of an annual fee and the performance by each applicant, referred to as a discharger, of certain obligations. These obligations include the following: (a) preparation of a site map of the property in question, starting with the roof each building on the property, showing the flow path of storm water runoff from the roof to the ground, then across the ground into the drain system on the property, and then from the property drain system into the public storm drain system; (b) visual observation of storm water discharge from the property during both the wet season (October through April) and the dry season (May through September); (c) submission of an estimate or calculation of the storm water discharge volume during two significant storm events in the wet season; (d) submission, for approval, of a proposed storm water sampling program; (e) execution of the approved storm water sampling program in compliance with the state regulations to obtain certain storm water samples; and (f) submission of the storm water samples for analysis.
Requirement (e) above of the Industrial Storm Water Permitting Program dictates that storm water samples be obtained during two separate storm events of the wet season and that one of these events be the first storm event of the wet season which produces significant storm water runoff preceded by at least 72 hours of dry weather. The storm water samples collected during each storm event must include a "grab sample" and a "composite". A grab sample in a storm water sample taken during the first thirty minutes of the discharge (or within the first hour of the discharge with explanation). A composite sample may be a sample taken with a continuous sampler or the combination of at least three grab samples taken during each hour of discharge with the successive grab samples being separated by a minimum period of at least 15 minutes. A composite sample shall be either flow-weighted (i.e. consist of a mixture of aliquots collected at constant time intervals, where the volume of each aliquot is proportional to the flow rate of the discharge) or time-weighted (i.e. consist of a mixture of equal volume aliquots collected at constant time intervals). Grab samples are used for determining certain specific contamination levels. Composite samples are used to obtain an estimate of average runoff water quality.
From the above discussion, it is evident that storm water sampling in compliance with the above-stated requirements of the Industrial Storm Water Permitting Program presents two basic problems. These problems are (a) having a storm water sampler in proper sampling readiness and position at the start of the first significant storm event of a wet season to collect a sample of the storm water runoff during the first 30 minutes of the discharge which will qualify as a valid "grab sample", and (b) having a storm water sampler in proper sampling readiness and position at the start of the first storm event of a wet season to collect a sample or samples of the storm water discharge during the first 3 hours of the discharge which will qualify as a valid "composite sample".
One way in which such valid grab and composite samples may be assured, of course, is to have persons standing by 24 hours a day during each and every day preceding the wet season in constant readiness to place storm water samplers in proper sampling positions immediately upon the start of each storm event to be monitored.
Obviously, this is an impractical solution to the storm water sampling problem. Moreover, there are numerous other situations in which liquid sampling is desirable or essential and which involve essentially the same or other similar sampling problems and requirements as storm water runoff sampling. Accordingly, there is a definite need for liquid sampling methods and devices for these and other liquid sampling purposes.